It is known to produce elemental chlorine by the reaction of gaseous hydrogen chloride with elemental oxygen, the so-called Deacon reaction. Moreover, such process can be combined with a process of chlorination wherein gaseous HCl and elemental oxygen are passed in vapor phase in contact with organic material to be chlorinated, under conditions such that the hydrogen chloride is oxidized with production of elemental or nascent chlorine which functions as a chlorinating agent. Such process is known as "oxyhydrochlorination" or "OHC."
The consumption of chlorine in the OHC process promotes oxidation of further quantities of the hydrogen chloride reactant. Representative of the earlier art in this area is an article in the publication, The Chemical Engineer, for July-August 1963 at pages 224-232 by J. T. Quant et al. A catalyst is used in such processes, especially copper chloride upon a carrier, usually a silicious carrier. Usually the catalyst is promoted by another metal chloride, especially alkali metal chloride, and/or rare earth metal chloride. For chlorination of alkanes and chloroalkanes, the temperature range employed is broadly from 350.degree. C. to 550.degree. C.; and for alkenes the broad temperature range is 200.degree. C. to 350.degree. C. Ordinarily, the elemental oxygen is supplied as oxygen of air, although the process is operative with more concentrated forms of elemental oxygen. Pressures used are generally about atmospheric, but can be higher, e.g. up to about 10 atmospheres.
In a modification of the "OHC" process just mentioned, fluorination can be effected upon a substance containing CCl groups, susceptible of fluorination by action of hydrogen fluoride. Hydrofluorination of chlorocarbons has been described using several catalyst systems, e.g. chromium oxyfluoride (British Pat. No. 1,025,759), chromium fluoride (U.S. Pat. No. 2,576,823 and British Pat. No. 640,486), iron chloride (British Pat. No. 640,486), thorium fluoride (U.S. Pat. No. 3,183,276), and antimony halides (U.S. Pat. No. 2,024,095). Hydrogen chloride under these reaction conditions may be returned to the oxychlorination process. A variant is to expose a hydrocarbon susceptible of chlorination to gaseous HCl and elemental oxygen under conditions suitable for oxyhydrochlorination; and to include hydrogen fluoride in the vapor phase to react with the chlorinated organic hydrocarbon formed. Such process is known as "oxychlorofluorination" or "OCF.".
A representative disclosure of an OCF process is in British Pat. No. 745,818, issued Mar. 7, 1956. In that patent the catalyst is aluminum fluoride impregnated with cupric chloride. Whitman U.S. Pat. No. 2,578,913, issued Dec. 18, 1951, relates to a somewhat similar fluorination process using in most examples a catalyst of copper oxide supported on alumina; and disclosing also (column 5, lines 23-35) use of oxides or salts of metals such as copper, lead, chromium, and iron group metals supported on alumina, calcium fluoride, or copper gauze; also copper chromite. Also of interest in U.S. Pat. No. 3,476,817, issued Nov. 4, 1969, which discloses a chlorofluorination reaction in which a hydrocarbon is reacted with chlorine in the presence of HF, a Deacon-type catalyst, and oxygen in an amount sufficient to improve the catalyst life. Other patents of interest include U.S. Pat. Nos. 3,379,780 and 3,398,203.
Problems which have been encountered in employing either the "OHC" or "OCF" process commercially arise from the fact that the copper chloride has enough vapor pressure at the required temperatures so that it migrates by sublimation. If in order to reduce the temperature required for reaction, the copper chloride is admixed with promoter salts such as potassium chloride, lithium chloride, rare earth metal chlorides and the like, eutectic compositions are formed which melt at the reaction temperature generally required for these processes and tend to coalesce. Consequently the known catalysts for OHC and OCF reactions show markedly decreasing catalytic effectiveness with continuing use.
Attempts have been made to minimize these problems by obtaining more active catalysts, which would operate at lower temperatures than usually required; or by obtaining the copper catalyst in a stabilized active form, sufficiently stable at the reaction temperatures to avoid sublimation and melting during use. These prior efforts have not been sufficiently successful, so far as we are aware, to allow the general commercialization of such processes under existing economic conditions.
An additional aspect significant from a commercial standpoint is the reactivity of the promoted copper chloride catalysts towards the materials of construction which would normally be considered for use under OHC and OCF reaction conditions. Inconel 600, a material of construction one would consider for such use, was found to be attacked by the metal halide component of the catalyst at 400.degree. C. at a corrosion rate of about 6 inches per year -- a corrosion rate obviously unacceptable from a commercial standpoint.